Gray Grunt

It exists only inside Martian Madness, so it has no spawn conditions of its own beyond the event running. That event is gated behind Golem: a Martian Probe has to find you in the outer thirds of the map and escape with the scan before the invasion arrives. Grunts are the filler of the roster, showing up in numbers between the things genuinely trying to kill you.

The one mechanical quirk is knockback immunity. A weapon you were using to hold a corridor will not push these back at all, so they walk through your line and into contact range. Killing them is still worth the ammunition, since they roll the same rare invasion loot as the heavier Martians, including the Charged Blaster Cannon and the Laser Drill. A farm that mows down cheap spawns is not wasting its time.

The sprite is the archetypal Gray of abduction folklore, the shape that entered popular culture through the Hill interviews and Roswell. Its bestiary line insists these are conscripts sent out with no weapons at all, which sits awkwardly beside a drop table containing a blaster cannon.